1 Musculoskeletal Statistics Unit, The Parker Institute, Department of Rheumatology, Bispebjerg and Frederiksberg Hospital, Copenhagen, Denmark; robin.christensen@regionh.dk.
2 Medicine Service, Birmingham VA Medical Center, Department of Medicine at School of Medicine, and Division of Epidemiology at School of Public Health, University of Alabama, Birmingham, AL; and Department of Orthopedic Surgery, Mayo Clinic College of Medicine, Rochester, MN, USA;
3 University of Ottawa Heart Institute, Ottawa, Canada;
4 School of Epidemiology, Public Health and Preventive Medicine, University of Ottawa, Ottawa, Canada.